Field of the Invention
This invention is directed to a modified epoxy resin, and more specifically, to a novel modified epoxy resin having improved flexibility and curing properties which can be effectively utilized in a powder coating, and a process for making such a modified epoxy resin.
Powder coatings are finding a wider use because of their good hygienic qualities and economical advantages. Powder coatings of epoxy resin type, however, had only limited applications since they had poor flexibility.
Generally, it is relatively easy to impart flexibility to solvent type coatings since various flexibilizers and softeners, which are usually liquid, can be employed in this type of coatings. These liquid flexibilizers and softeners as such can not be employed in powder coatings.
Solid type flexibilizers are also known. These solid type flexibilizers, however, are incompatible with high molecular weight epoxy resin while they are compatible with liquid type epoxy resin. There is thus a need for a flexible epoxy resin.
On the other hand, a reduction in baking time of the powder coatings is desired for improving the productivity, although baking at high temperature is undesirable for an economical reason. An addition of an increased amount of curing agent is also undesirable since the resulting increased amount of free components in the coating after its curing may adversely affect the chemical resistance of the coating.
After an investigation to overcome the above-described defects, the inventors of the present invention have found that, by subjecting the epoxy resin to a reaction with a primary amine, the chain may be extended to thereby improve the curing properties, and by reacting the epoxy resin with a lactone, some of secondary hydroxyl groups may undergo a ring opening polymerization by which an appropriate flexibility is imparted to the hard, fragile epoxy resin.
It is therefore an object of this invention to provide a novel modified epoxy resin which has both appropriate flexibility and curing properties.
It is a further object of this invention to provide a process for preparing the novel modified epoxy resin.
Other objects and advantage of the invention will become apparent as the description thereof proceeds.